366 DONALD C. BARTON 
chert examined the transition was distinctly sharp, being confined 
to a zone of 0.2 to o.4 millemeters in width. 
The lateral contacts of the larger, semispherical nodules can be 
seen in many cases to be zones of slight displacement. The lines 
of stratification running into or across the chert are broken and 
slightly displaced upward, the more so toward the top of the nodule, 
and not at all or only faintly in reverse at the base. The ends of 
the line of stratification in the adjoining limestone in many cases 
tl 
HANG /, 
ra ees 
Fic. 2.—Chert from the St. Louis limestone, St. Louis, Missouri, under the high 
power: a, chalcedony; 6, dolomite rhombs; c, limonite stain; d, granular quartz; 
é, silicified shell; f, microgranular groundmass. 
are bent up near the nodule with the upper ones arching over, but 
in other cases run to the contact without deviation. Slickensides 
were found in a very few cases on the lateral contacts, showing 
relative movement upward of the chert of the nodule. 
CHARACTER OF THE ROCK INCLOSING THE CHERT 
Although chert is confined to calcareous rocks, the exact char- 
acter of the rock in which chert appears varies widely. The grain 
seems to have no effect on the presence of chert, which is found 
